The present invention relates to processes for the production of high crimp, high strength, hollow rayon fibers or filaments which will recover their hollow condition after being immersed in water and are substantially irreversible in that they will remain hollow and do not collapse even after repeated drying and washing cycles. These fibers will also possess high crimp of at least about 20 crimps per inch, preferably 25-30 crimps per inch, when immersed in water and dried in a tension-free state. The invention relates also to the high crimp hollow rayon fibers produced.
Hollow rayon fibers are known to the prior art. They have a number of known uses in the production of paper and non-woven products. They have been produced by incorporating a blowing agent, such as sodium carbonate or sodium bicarbonate, into the viscose rayon process. In the prior art processes, the viscose, containing the blowing agent, is spun into the conventional acidic spin bath whereby carbon dioxide gas is liberated from the blowing agent causing the fibers to blow or expand to several times their natural diameter.
A number of patents disclose processes of this type, and they have the shortcoming that when the fibers or filaments are dried, the fiber walls collapse, and, in most instances, hydrogen bond together to form a flat, ribbon-like fiber. Other processes that produce a substantially irreversible hollow fiber have the shortcoming of possessing inadequate crimp such that the fibers are difficult to blend with other fibers and have poor carding capability (fibers do not cling well enough to each other to form a sufficiently strong web for processing into yarn). It is the desire of the rayon industry to provide hollow rayon fibers which will not collapse upon drying and have sufficient crimp for processing through the carding operation and for blending uniformly with other fibers.
Woodings U.S. Pat. No. 3,626,045 is a patent disclosing a method of blowing rayon fibers. It seeks to overcome the problem of fiber wall collapse upon drying by adding to the viscose prior to spinning of from 0.75-2.0 percent by weight of polyethylene glycol based on the weight of the cellulose. The hollow rayon fibers which result can be dried after being formed without collapsing. However, the product of the patent possesses low crimp of about 12 crimps per inch which has been reported to be difficult to card and blend with other fibers.
Patents disclose various methods for making hollow fibers, but none of which applicants are aware teaches or suggests a means which provides a high strength hollow rayon fiber which is substantially irreversible in the sense that it will not collapse upon being dried. These patents include: British Pat. No. 945,306; British Pat. No. 1,393,778; and Freund U.S. Pat. No. b 2,013,491.
British Pat. No. 488,500 discloses a process for producing hollow cellulose acetate fibers by extruding a solution of the acetate downward into a volatile solvent medium and in a complicated manner produces a hollow fiber.
Kajitani U.S. Pat. No. 3,418,405 discloses a process for producing flat viscose fibers by extruding blown viscose into a medium containing a modifier, and such modifier is polyethylene glycol. The whole purpose is to produce a hollow fiber which will very readily collapse and form a flat fiber. This is just the opposite of the purpose of the present invention.
British Pat. No. 1,393,778 discloses the preparation of multi-lobal collapsed fibers, which is not what the present invention is concerned with, by a process which is quite different from that of the present invention.
Kobuta et al. Japanese patent publications Nos. 9536 and 9537 are patents describing a process for producing hollow rayon fibers. These processes do not employ sodium carbonate nor sodium bicarbonate nor any other chemical that when in contact with the acidic spin bath will liberate a blowing agent. But rather, this concept employs the evolved CS.sub.2 during decomposition in the spin bath as a blowing agent. Because this is a slow blowing process, surfactants are needed so as to reduce the surface tension and allow large bubbles to form. Not only is this process for making hollow fibers quite different, but also it is not one that will produce a high crimp hollow fiber.
Japanese patent publication No. 20164 describes a high crimp solid rayon fiber with high water resistance. This process does not claim a hollow rayon fiber, but rather a solid rayon fiber; furthermore, it teaches away from the process of this invention because it stresses the use of low CS.sub.2, i.e., 26-32 percent on the weight of cellulose. It achieves high crimp by using various assistant agents such as monoamines, alkylene oxide polymers and bivalent metallic compounds in combination with the process conditions.
Daul et al. U.S. Pat. Nos. 3,632,468 and 3,793,136 also describe a process for making a high crimp solid rayon fiber. This concept does not involve the production of hollow rayon fibers but only high crimp solid rayon fibers. It seeks to develop high crimp by an alkaline treatment while the fibers are in a relaxed state after they have been stretched and partially regenerated. This concept is quite removed from the process described in our invention. Similarly, Stevens U.S. Pat. No. 3,720,743 also discloses the productin of high crimp solid rayon fibers and is remote from the present invention.
In accordance with the present invention, the disadvantages of conventional prior art blown hollow rayon fibers have been overcome by unique conditions of the processes of the present invention. These parameters are discussed below and are employed in the examples which follow.
In copending U.S. application Ser. No. 798,874, filed May 20, 1977, now U.S. Pat. No. 4,130,689, granted Dec. 19, 1978, by one of us, namely, Eugene Costa, Jr., there is disclosed a process for producing superior hollow rayon fibers which do not collapse when dried and washed. However, the hollow rayon fibers of said application do not have the high degree of crimp which characterizes the hollow rayon fibers of the present invention. The fibers possess about 12 crimps per inch.
The hollow fibers of rayon produced by the processes of the invention do not collapse even when dried and will not collapse even when subjected to a sequence of drying and washing treatments. The processes also produce a uniformly large number of blown fibers such as more than 90 or 95 percent of all fibers being hollow or blown.
The fibers produced not only have permanent hollowness, but also exhibit high strength and high crimp to permit ease in carding and uniformity in blending with other fibers. The fibers produced by the processes of the present invention have properties similar to commercial high wet modulus rayon and are approaching that of cotton.
It is, accordingly, an objective of the present invention to provide an in-line process for producing hollow rayon fibers of high strength that have the property of resisting collapse even after drying and washing treatments, which have large continuous lumens, and which possess high crimp, that is, in excess of about 20 crimps per inch with the average being between about 25 and 30 crimps per inch.
It is also an object of the present invention to provide hollow rayon fibers that have high bulk or covering power such as are useful in producing non-wovens or garments for outer wear.
It is a further object of the present invention to provide hollow rayon fibers that have a soft, comfortable hand and which will retain their hollow condition after being immersed in water and then dried.
It is another object of the present invention to provide hollow rayon fibers which have high moisture absorption, thermal insulation and dielectric properties.
It is another object of this invention to produce fibers of high strength having greater than 3.0 g/d (grams per denier) tenacity when tested in a conditioned atmosphere and greater than 1.5 g/d when tested in a wet state.
Other objects will be apparent to those skilled in the art from the present description and the appended drawing which is a photomicrograph of a collection of hollow fibers in accordance with the present invention magnified 1500 times, showing the hollow structure of the fibers.